In response to the recent demand for very fine processing techniques in the field of semiconductor manufacturing, dry etching has become mainstream in place of wet processing. The dry etching is a technique for forming a fine pattern on a molecular basis on a material surface by generation of plasma in a vacuum space.
For etching of semiconductor material e.g. silicon dioxide (SiO2), perfluorocarbon (PFC) and hydrofluorocarbon (HFC) compounds such as CF4, CHF3, C2F6, C3F8 and C4F8 have been used as etching agents in order to increase the etching rate of SiO2 relative to substrate material e.g. silicon, polysilicon or silicon nitride. However, these PFC and HFC compounds are specified as emission control materials in the Kyoto protocol (COP3) because each of these PFC and HFC compounds has a long atmospheric lifetime and a high global warming potential (GWP). The semiconductor industry thus has a demand for alternative low-GWP materials of high cost efficiency and capable of fine processing.
Patent Document 1 discloses the use of a reactive gas containing a C4-C7 perfluoroketone as a cleaning gas or etching gas in place of PFC of HFC gas. This reactive gas is not however always favorable as the etching gas due to the fact that, when the C4-C7 perfluoroketone gets decomposed, the resulting decomposition product contains a considerable amount of high-GWP PFC compound and relatively high-boiling substances.
Patent Document 2 discloses the use of a C2-C6 hydrofluoroether as a dry etching gas. However, the C2-C6 hydrofluoroether is generally high in GWP and is not favorable in terms of global environmental perspective as in the case of Patent Document 1.
Under the above circumstances, there has been a demand to develop lower-GWP compounds industrially easy to produce. In particular, it has been examined to apply unsaturated fluorocarbons having a double or triple bond in their respective molecules for etching process.
As a technique relevant to such application, Patent Document 3 discloses a method of etching a Si film, a SiO2 film, a Si3N4 film or a high-melting metal silicide film with the use of an ether such as CaF2a+1OCF═CF2 or a fluorinated olefin such as CF3CF═CFH or CH3CH═CH2.
Further, Patent Document 4 discloses a plasma etching method using hexafluoro-2-butyne, hexafluoro-1,3-butadiene, hexafluoropropene or the like as an etching gas.
Patent Document 5 discloses a method of etching an oxide layer on a non-oxide layer e.g. nitride layer with the use of a mixed gas containing: (a) an unsaturated fluorocarbon selected from the group consisting of hexafluorobutadiene, octafluoropentadiene, pentafluoropropene and trifluoropropyne; (b) a hydrofluoro methane such as monofluoromethane or difluoromethane; and (c) an inert carrier gas.
Patent Document 6 discloses the use of a C5-C6 acyclic perfluoroalkyne as a plasma reaction gas. Patent Document 7 discloses a method of producing a perfluoroalkene compound suitable for use as a dry etching gas or CVD gas and as a raw material of fluorine-containing polymers.
Patent Document 8 discloses the use of 1,3,3,3-tetrafluoropropene as an assist gas in laser-assisted etching. The laser-assisted etching is a technique of etching a material with an etchant by thermal activation of the material and excitation of the etchant under irradiation of a laser light and is basically different in excitation means from the dry etching in which a reactive gas is generated by the action of electric energy to react with a substrate and form a desired shape on the substrate.
Patent Document 9 discloses the use of a gas containing 2,3,3,3-tetrafluoropropene as an etching gas for a silicon oxide film. Herein, 2,3,3,3-tetrafluoropropene has also been developed as a coolant for a car air conditioner and exhibits a combustion range in a dry condition at ambient temperature (as measured according to ASTM E681-04). On the other hand, 1,3,3,3-tetrafluoropropene does not exhibit a combustion range under the same measurement conditions and thus can be regarded as a higher safety material.
Furthermore, Non-Patent Document 1 discloses the use of a straight-chain unsaturated compound such as hexafluoropropene or hexafluorobutadiene for etching of silicon oxide material.